Many manufacturing operations require that precise dimensions be maintained between various parts of production machinery. For example, in roll coating operations required during the manufacture of photographic film, subbing, or overcoat layers are applied to a moving web as the web passes through a coating station. The subbing layer thickness is controlled by passing the coated web through a gap formed by a pair of rollers. The gap spacing, and thus the thickness of the subbing layer, varies due to thermal expansion and contraction of the rollers as the rollers change temperature.
A conventional method of measuring the gap between rollers is performed using shims. These measurements take place while the rollers are stationary, with the machinery at a temperature other than its normal operating temperature, and with the access doors to the machinery open. Unfortunately, this conventional technique does not provide real-time measurement of the roller gap while the machinery is actually operating. Production quality could be improved if the gap between the rollers could be monitored in real time, while the machinery is at normal operating temperatures, and while the product is actually being manufactured.
Furthermore, in many manufacturing processes, such as photographic film subbing, flammable solvents are present. The presence of electrical signals in such an environment creates the possibility of fire or an explosion.